The invention relates to an apparatus for generating ultrasonic fields. The ultrasound is generated according to the thermohydraulic principle in liquids. The apparatus has at least two electrodes which enclose a volume with an electrolyte and are driven by a power pulse generator, and a sound transmitter surface.
Ultrasound is used in a wide variety of technological applications and, furthermore, especially in medicine. Examples of medical applications are imaging diagnosis methods in medicine, such as the ultrasonic examination of internal organs and of fetuses in pregnant women. Examples of general technology are the crack-fracture point localization of highly stressed parts or sonar methods.
Over and above the aforementioned applications, intensive focused ultrasonic fields, especially, have been used relatively recently in hypothermia methods in medical treatment and in surgery. Preconditions here include a high spatial resolution and good focusability. To those ends, it is necessary to generate high frequencies in the range above 1 MHz in conjunction with time-averaged sonic powers of a few watts up to a few 100 watts. The quality of the wavefront of the ultrasonic field is of great importance for the resolution and focus size.
Systems that have been introduced in practical applications predominantly utilize piezoelectric sound transducers, which are well suited to generating plane wavefronts. Focusing is thereby effected either by acoustic lenses or else by specific shaping of the sound transducers. Multidimensional arrays are also known, these having been developed for example as phase-controlled arrangements (phased arrays), in which the individual elements can be driven independently of one another in order to control the focus position and focus size in a targeted manner by changing electrical parameters.
The construction of the prior art assemblies is comparatively complex, and the service life of the sound transducers and the amplitudes that can be achieved leave something to be desired.
We have previously considered utilizing the thermohydraulic principle for generating intensive pressure pulses in liquids in order to generate ultrasonic wave fields. Information in that regard may be found in the commonly assigned published German patent application DE 19 702 593 A1 (not prior art). There, an electrolyte layer located between two electrodes is heated by a power pulse having a short duration, and an intensive pressure wave is radiated on account of the volumetric expansion of the electrolyte, associated with the heating, into the adjoining medium. The generation of individual pressure pulses according to this method makes it possible to generate plane wavefronts, or wavefronts shaped virtually as desired, with amplitudes of a number of MPa. However, this requires electrical pulses having peak powers in the neighborhood of about 100 MW.
It is accordingly an object of the invention to provide an apparatus for generating ultrasonic fields, which overcomes the disadvantages of the heretofore-known devices and methods of this general type and which, taking the previous development as a departure point, provides for a practical apparatus for generating ultrasonic fields.
With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for generating ultrasonic fields by the thermohydraulic principle in liquids, comprising:
at least two electrodes and a volume with an electrolyte enclosed by the electrodes;
a power pulse generator connected to and driving the electrodes for heating the electrolyte volume;
a sound transmitter surface; and
semiconductor switching elements connected to the power pulse generator, whereby the electrolyte volume to be heated by an electrical pulse emitted by the power pulse generator is delimited to such an extent that an electrical power is controlled by the semiconductor switching elements.
In other words, the objects of the invention are satisfied in that the electrolyte volume to be heated by the electrical pulse is delimited to such an extent that the electrical power to be applied can be handled by semiconductor switching elements. In this case, the sound transmitter surface may preferably be provided either as a two-dimensional array with defined array elements or else as a one-and-a-half-dimensional arrangement of array elements.
The novel sound transmitter surface is structured in such a way that the individual elements have correspondingly small dimensions. Such elements are also referred to as xe2x80x9cactelsxe2x80x9d (actuator-elements). An ultrasonic field having a high average power can thus be generated by the application of high pulse repetition rates. It is particularly advantageous that a ultrasonic wavefront can be shaped virtually as desired by targeted driving of the individual actels. The average heat loss converted in the electrolyte in the process can be dissipated by cooling, with the result that stable conditions are manifested over lengthy application periods.
In accordance with an added feature of the invention, the semiconductor switching elements are transistors or thyristors, and in particular field-effect transistors.
In accordance with an additional feature of the invention, the sound transmitter surface is structured as a two-dimensional array with individually driven defined array elements.
In accordance with another feature of the invention, the sound transmitter surface is structured as a phase-controlled array, with individual array elements having corresponding dimensions.
In accordance with a further feature of the invention, the sound transmitter surface is a one-and-a-half-dimensional arrangement of individually driven array elements for generating cylindrical wavefronts or spherical wavefronts.
In accordance with again an added feature of the invention, the sound transmitter surface is an array of individually driven array elements arranged on a curved surface.
In accordance with again an additional feature of the invention, there is provided an electronic drive unit for driving the array elements simultaneously, but independently of one another. In an alternative embodiment, the electronic drive unit drives the array elements with predeterminable time differences.
In accordance with again another feature of the invention, one of the electrodes is a carrier electrode and a portion of the electronic drive unit is integrated directly on the carrier electrode, such as driver transistors or a diode matrix.
In accordance with a concomitant feature of the invention, there are provided spacer elements for delimiting the electrolyte volume and, at the same time, for forming spacers between the electrodes.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an apparatus for generating ultrasonic fields, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.